Variable magnification optical system, optical equipment, imaging equipment and method for manufacturing variable magnification optical system

ABSTRACT

A variable magnification optical system comprises, in order from an object side, a first lens group G 1  having positive refractive power, a second lens group G 2  having negative refractive power, a third lens group G 3  having positive refractive power and a fourth lens group G 4  having negative refractive power; upon varying a magnification, a distance between the first lens group G 1  and the second lens group G 2  being varied, a distance between the second lens group G 2  and the third lens group G 3  being varied, and a distance between the third lens group G 3  and the fourth lens group G 4  being varied; upon focusing, the fourth lens group G 4  being moved; and a predetermined conditional expression being satisfied. With such a configuration, there is provided a variable magnification optical system whose focusing lens group is compact in size and reduced in weight, so high speed and quiet focusing can be effected without lens barrel being made large in size, and further by which variations in aberrations upon varying magnification from the wide angle end state to the telephoto end state as well as variations in aberrations upon focusing from the infinite distance object to the close distance object can be superbly suppressed.

TECHNICAL FIELD

The present invention relates to a variable magnification opticalsystem, an optical equipment, an imaging equipment, and a method formanufacturing the variable magnification optical system.

BACKGROUND ART

Conventionally, there have been proposed a variable magnificationoptical system which is suitable for a photographing camera, anelectronic still camera, a video camera or the like. See, for example,Japanese patent application Laid-Open Gazette No. H4-293007. However,with respect to conventional variable magnification optical system,weight reducing has not been taken in consideration sufficiently.

PRIOR ART REFERENCE Patent Document

Patent Document 1: Japanese patent application Laid-Open Gazette No.H4-293007

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda variable magnification optical system comprising, in order from anobject side: a first lens group having positive refractive power, asecond lens group having negative refractive power, a third lens grouphaving positive refractive power, and a fourth lens group havingnegative refractive power; and

upon varying a magnification, a distance between the first lens groupand the second lens group being varied, a distance between the secondlens group and the third lens group being varied, and a distance betweenthe third lens group and the fourth lens group being varied;

upon focusing, the fourth lens group being moved; and the followingconditional expressions being satisfied:0.55<f2/f4<1.401.40<f1/fw<2.80

where f1 denotes a focal length of the first lens group; f2 denotes afocal length of the second lens group; f4 denotes a focal length of thefourth lens group; and fw denotes a focal length of the variablemagnification optical system in the wide angle end state.

According to a second aspect of the present invention, there is provideda method for manufacturing a variable magnification optical system, themethod comprising step of arranging, in order from an object side: afirst lens group having positive refractive power, a second lens grouphaving negative refractive power, a third lens group having positiverefractive power, and a fourth lens group having negative refractivepower, such that, upon varying a magnification, a distance between thefirst lens group and the second lens group being varied, a distancebetween the second lens group and the third lens group being varied, anda distance between the third lens group and the fourth lens group beingvaried;

upon focusing, the fourth lens group being moved; and

the following conditional expressions being satisfied:0.55<f2/f4<1.401.40<f1/fw<2.80

where f1 denotes a focal length of the first lens group; f2 denotes afocal length of the second lens group; f4 denotes a focal length of thefourth lens group; and fw denotes a focal length of the variablemagnification optical system in the wide angle end state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a variable magnification opticalsystem according to a First Example.

FIG. 2 are graphs showing various aberrations of the variablemagnification optical system according to the First Example.

FIG. 3 are graphs showing meridional transverse aberrations of thevariable magnification optical system according to the First Example.

FIG. 4 are graphs showing various aberrations of the variablemagnification optical system according to the First Example.

FIG. 5 is a sectional view showing a variable magnification opticalsystem according to a Second Example.

FIG. 6 are graphs showing various aberrations of the variablemagnification optical system according to the Second Example.

FIG. 7 are graphs showing meridional transverse aberrations of thevariable magnification optical system according to the Second Example.

FIG. 8 are graphs showing various aberrations of the variablemagnification optical system according to the Second Example.

FIG. 9 is a sectional view showing a variable magnification opticalsystem according to a Third Example.

FIG. 10 are graphs showing various aberrations of the variablemagnification optical system according to the Third Example.

FIG. 11 are graphs showing meridional transverse aberrations of thevariable magnification optical system according to the Third Example.

FIG. 12 are graphs showing various aberrations of the variablemagnification optical system according to the Third Example.

FIG. 13 is a sectional view showing a variable magnification opticalsystem according to a Fourth Example.

FIG. 14 are graphs showing various aberrations of the variablemagnification optical system according to the Fourth Example.

FIG. 15 are graphs showing meridional transverse aberrations of thevariable magnification optical system according to the Fourth Example.

FIG. 16 are graphs showing various aberrations of the variablemagnification optical system according to the Fourth Example.

FIG. 17 is a view showing a configuration of a camera equipped with thevariable magnification optical system.

FIG. 18 is a flowchart schematically showing a method for manufacturingthe variable magnification optical system.

EMBODIMENT FOR CARRYING OUT THE INVENTION

A variable magnification optical system, an optical equipment, animaging equipment and a method for manufacturing the variablemagnification optical system according to the embodiment of the presentinvention is described below.

The variable magnification optical system according to the presentembodiment comprises, in order from an object side, a first lens grouphaving positive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having negative refractive power;

upon varying a magnification, a distance between the first lens groupand the second lens group being varied, a distance between the secondlens group and the third lens group being varied, and a distance betweenthe third lens group and the fourth lens group being varied;

upon focusing from an infinite distance object to a close distanceobject, the fourth lens group being moved; and

the following conditional expressions (1) and (2) being satisfied:0.55<f2/f4<1.40  (1)1.40<f1/fw<2.80  (2)

where f1 denotes a focal length of the first lens group; f2 denotes afocal length of the second lens group; f4 denotes a focal length of thefourth lens group; and fw denotes a focal length of the variablemagnification optical system in the wide angle end state.

The variable magnification optical system according to the presentembodiment comprises at least four lens groups, as described above, andcan correct superbly aberrations upon varying magnification by varyingrespective distances between the lens groups upon varying magnification.

Further, in the variable magnification optical system according to thepresent Embodiment, as described above, the fourth lens group is made tobe a focusing lens group, thereby the focusing lens group being madecompact in size and reduced in weight.

The conditional expression (1) defines a ratio of the focal length ofthe second lens group to the focal length of the fourth lens group. Withsatisfying the conditional expression (1), the variable magnificationoptical system according to the present embodiment can suppressvariations in spherical aberration and other various aberrations uponvarying magnification from the wide angle end state to the telephoto endstate. Further, upon focusing from an infinite distance object to aclose distance object, variations in spherical aberration and othervarious aberrations can be suppressed.

When the value of f2/f4 of the variable magnification optical systemaccording to the present embodiment is equal to or exceeds the upperlimit value of the conditional expression (1), the refractive power ofthe fourth lens group becomes large, and as a result, it becomesdifficult to suppress variations in spherical aberration and othervarious aberrations upon focusing from an infinite distance object to aclose distance object. Meanwhile, in order to attain the advantageouseffect of the present embodiment surely, it is preferable to set theupper limit value of the conditional expression (1) to 1.35. Also, inorder to attain the advantageous effect of the present embodiment moresurely, it is preferable to set the upper limit value of the conditionalexpression (1) to 1.30.

On the other hand, when the value of f2/f4 of the variable magnificationoptical system according to the present embodiment is equal to or fallsbelow the lower limit value of the conditional expression (1), therefractive power of the second lens group becomes large, and it becomesdifficult to suppress variations in spherical aberration and othervarious aberrations upon varying magnification from the wide angle endstate to the telephoto end state. Meanwhile, in order to attain theadvantageous effect of the present embodiment surely, it is preferableto set the lower limit value of the conditional expression (1) to 0.58.Also, in order to attain the advantageous effect of the presentembodiment more surely, it is preferable to set the lower limit value ofthe conditional expression (1) to 0.60.

The conditional expression (2) defines a ratio of the focal length ofthe first lens group to the focal length of the variable magnificationoptical system in the wide angle end state. With satisfying theconditional expression (2), a lens barrel of the variable magnificationoptical system according to the present embodiment can be prevented frombeing large in size and it becomes possible to suppress variations inspherical aberration and other various aberrations upon varyingmagnification from the wide angle end state to the telephoto end state.

When the value of f1/fw of the variable magnification optical systemaccording to the present embodiment is equal to or exceeds the upperlimit value of the conditional expression (2), the refractive power ofthe first lens group becomes small, and as a result, the lens barrelbecomes large in size. Meanwhile, in order to attain the advantageouseffect of the present embodiment surely, it is preferable to set theupper limit value of the conditional expression (2) to 2.70. Also, inorder to attain the advantageous effect of the present embodiment moresurely, it is preferable to set the upper limit value of the conditionalexpression (2) to 2.60.

On the other hand, when the value of f1/fw is equal to or falls belowthe lower limit value of the conditional expression (2), the refractivepower of the first lens group becomes large, and as a result, it becomesdifficult to correct spherical aberration and other various aberrationsupon varying magnification from the wide angle end state to thetelephoto end state. Meanwhile, in order to attain the advantageouseffect of the present embodiment surely, it is preferable to set thelower limit value of the conditional expression (2) to 1.50. Also, inorder to attain the advantageous effect of the present embodiment moresurely, it is preferable to set the lower limit value of the conditionalexpression (2) to 1.60.

With such construction as described, it is possible to realize avariable magnification optical system whose focusing lens group iscompact in size and reduced in weight, so high speed and quiet focusingcan be effected without lens barrel being made large in size, andfurther by which variations in aberrations upon varying magnificationfrom the wide angle end state to the telephoto end state as well asvariations in aberrations upon focusing from the infinite distanceobject to the close distance object can be superbly suppressed.

Further, it is desirable that the variable magnification optical systemaccording to the present embodiment satisfies the following conditionalexpression (3):0.82<(−f2)/f3<1.30  (3)

where f3 denotes a focal length of the third lens group.

The conditional expression (3) defines a ratio of the focal length ofthe second lens group to the focal length of the third lens group. Withsatisfying the conditional expression (3), the variable magnificationoptical system according to the present embodiment can suppressvariations in spherical aberration and other various aberrations uponvarying magnification from the wide angle end state to the telephoto endstate.

When the value of (−f2)/f3 of the variable magnification optical systemaccording to the present embodiment is equal to or exceeds the upperlimit value in the conditional expression (3), the refractive power ofthe third lens group becomes large, and as a result, it becomesdifficult to suppress variations in spherical aberration and othervarious aberrations upon varying magnification from the wide angle endstate to the telephoto end state. Meanwhile, in order to attain theadvantageous effect of the present embodiment surely, it is preferableto set the upper limit value of the conditional expression (3) to 1.25.Also, in order to attain the advantageous effect of the presentembodiment more surely, it is preferable to set the upper limit value ofthe conditional expression (3) to 1.20.

On the other hand, when the value of (−f2)/f3 of the variablemagnification optical system according to the present embodiment isequal to or falls below the lower limit of the conditional expression(3), the refractive power of the second lens group becomes large, and itbecomes difficult to suppress variations in spherical aberration andother various aberrations upon varying magnification from the wide angleend state to the telephoto end state. Meanwhile, in order to attain theadvantageous effect of the present embodiment surely, it is preferableto set the lower limit value of the conditional expression (3) to 0.85.Also, in order to attain the advantageous effect of the presentembodiment more surely, it is preferable to set the lower limit value ofthe conditional expression (3) to 0.90.

Further, it is desirable that the variable magnification optical systemaccording to the present embodiment satisfies the following conditionalexpression (4):2.00<f1/(−f2)<4.00  (4)

The conditional expression (4) defines a ratio of the focal length ofthe first lens group to the focal length of the second lens group. Withsatisfying the conditional expression (4), the variable magnificationoptical system according to the present embodiment can suppressvariations in spherical aberration and other various aberrations uponvarying magnification from the wide angle end state to the telephoto endstate.

When the value of f1/(−f2) of the variable magnification optical systemaccording to the present embodiment is equal to or exceeds the upperlimit value in the conditional expression (4), the refractive power ofthe second lens group becomes large, and as a result, it becomesdifficult to suppress variations in spherical aberration and othervarious aberrations upon varying magnification from the wide angle endstate to the telephoto end state. Meanwhile, in order to attain theadvantageous effect of the present embodiment surely, it is preferableto set the upper limit value of the conditional expression (4) to 3.80.Also, in order to attain the advantageous effect of the presentembodiment more surely, it is preferable to set the upper limit value ofthe conditional expression (4) to 3.50.

On the other hand, when the value of f1/(−f2) of the variablemagnification optical system according to the present embodiment isequal to or falls below the lower limit value in the conditionalexpression (4), the refractive power of the first lens group becomeslarge, and it becomes difficult to suppress variations in sphericalaberration and other various aberrations upon varying magnification fromthe wide angle end state to the telephoto end state. Meanwhile, in orderto attain the advantageous effect of the present embodiment surely, itis preferable to set the lower limit value of the conditional expression(4) to 2.30. Also, in order to attain the advantageous effect of thepresent embodiment more surely, it is preferable to set the lower limitvalue of the conditional expression (4) to 2.60.

It is desirable that in the variable magnification optical system thefourth lens group consists of, in order from the object side, a positivelens and a negative lens. With such a configuration, the fourth lensgroup that is a focusing lens group can be reduced in weight andspherical aberration and other various aberrations upon varyingmagnification from the wide angle end state to the telephoto end state,can be suppressed.

Further, it is desirable that the variable magnification optical systemaccording to the present embodiment satisfies the following conditionalexpression (5):2.20<fP/(−fN)<3.70  (5)where fP denotes a focal length of the positive lens in the fourth lensgroup, and fN denotes a focal length of the negative lens in the fourthlens group.

The conditional expression (5) defines a ratio of the focal length ofthe positive lens in the fourth lens group to the focal length of thenegative lens in the fourth lens group. With satisfying the conditionalexpression (5), the variable magnification optical system according tothe present embodiment can suppress variations in coma aberration andother various aberrations upon focusing from the infinite distanceobject to the close distance object.

When the value of fP/(−fN) of the variable magnification optical systemaccording to the present embodiment is equal to or exceeds the upperlimit value of the conditional expression (5), the refractive power ofthe negative lens in the fourth lens group becomes large, and comaaberration becomes excessively generated. As a result, it becomesdifficult to suppress variations in coma aberration and other variousaberrations upon focusing from the infinite distance object to the closedistance object. Meanwhile, in order to attain the advantageous effectof the present embodiment surely, it is preferable to set the upperlimit value of the conditional expression (5) to 3.60. Also, in order toattain the advantageous effect of the present embodiment more surely, itis preferable to set the upper limit value of the conditional expression(5) to 3.50.

On the other hand, when the value of fP/(−fN) of the variablemagnification optical system according to the present embodiment isequal to or falls below the lower limit value of the conditionalexpression (5), the refractive power of the positive lens in the fourthlens group becomes large, and as a result, coma aberration isexcessively corrected. Therefore, it becomes difficult to suppressvariations in coma aberration and other various aberrations uponfocusing from the infinite distance object to the close distance object.Meanwhile, in order to attain the advantageous effect of the presentembodiment surely, it is preferable to set the lower limit value of theconditional expression (5) to 2.30. Also, in order to attain theadvantageous effect of the present embodiment more surely, it ispreferable to set the lower limit value of the conditional expression(5) to 2.40.

Further, in the variable magnification optical system according to thepresent embodiment it is desirable that, upon varying magnification, thefirst lens group is fixed in position with respect to the image plane.With this configuration, it is possible for the variable magnificationoptical system according to the present embodiment to carry out varyingmagnification from the wide angle end state to the telephoto end statewithout changing the total length thereof.

Further, in the variable magnification optical system according to thepresent embodiment it is desirable that, upon varying magnification, thethird lens group is fixed in position with respect to the image plane.With this configuration, it is possible to suppress deterioration inperformance of the variable magnification optical system according tothe present embodiment caused due to manufacturing error, thereby itbecoming possible to secure mass-productivity.

Further, in the variable magnification optical system according to thepresent embodiment it is desirable that the first lens group comprises,in order from the object side, a positive lens, a negative lens and apositive lens. With this configuration, it is possible to correcteffectively spherical aberration and coma aberration in the telephotoend state.

Further, it is desirable that the variable magnification optical systemaccording to the present embodiment comprises a vibration reduction lensgroup that is movable to have a displacement component in the directionperpendicular to the optical axis. With this configuration, it ispossible to correct displacement of the imaging position caused by acamera shake, that is, it is possible to carry out vibration reduction.

Further, it is desirable that the variable magnification optical systemaccording to the present embodiment satisfies the following conditionalexpression (6):0.70<|fvr|/f3<1.60  (6)

where fvr denotes a focal length of the vibration reduction lens group;and f3 denotes a focal length of the third lens group.

The conditional expression (6) defines a ratio of the focal length ofthe vibration reduction lens group to the focal length of the third lensgroup. With satisfying the conditional expression (6), the variablemagnification optical system according to the present embodiment cansuppress effectively deterioration in performance upon the vibrationreduction being conducted and also can suppress variations in sphericalaberration and other various aberrations.

When the value of |fvr|/f3 of the variable magnification optical systemaccording to the present embodiment is equal to or exceeds the upperlimit value in the conditional expression (6), the refractive power ofthe third lens group becomes large, and as a result, it becomesdifficult to suppress variations in spherical aberration and othervarious aberrations upon varying magnification from the wide angle endstate to the telephoto end state. Meanwhile, in order to attain theadvantageous effect of the present embodiment surely, it is preferableto set the upper limit value of the conditional expression (6) to 1.50.Also, in order to attain the advantageous effect of the presentembodiment more surely, it is preferable to set the upper limit value ofthe conditional expression (6) to 1.40.

On the other hand, when the value of |fvr|/f3 of the variablemagnification optical system according to the present embodiment isequal to or falls below the lower limit value in the conditionalexpression (6), the refractive power of the vibration reduction lensgroup becomes large, and it becomes difficult to correct decenteringcoma generated upon conducting the vibration reduction. Meanwhile, inorder to attain the advantageous effect of the present embodimentsurely, it is preferable to set the lower limit value of the conditionalexpression (6) to 0.80. Also, in order to attain the advantageous effectof the present embodiment more surely, it is preferable to set the lowerlimit value of the conditional expression (6) to 0.90.

The optical equipment according to the present embodiment of the presentinvention comprises the variable magnification optical system having aconfiguration as described above.

The imaging equipment according to the present embodiment of the presentinvention comprises the variable magnification optical system having theconfiguration as described above and an imaging section picking up animage formed through the variable magnification optical system.

With such configurations, it is possible to realize an optical equipmentand an imaging equipment, in which focusing lens group is compact insize and reduced in weight, so high speed and quiet focusing beingeffected without lens barrel being made large in size, and further bywhich variations in aberrations upon varying magnification from the wideangle end state to the telephoto end state as well as variations inaberrations upon focusing from the infinite distance object to the closedistance object can be superbly suppressed.

A method for manufacturing a variable magnification optical systemaccording to the present embodiment of the present invention, comprisesstep of arranging, in order from an object side: a first lens grouphaving positive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having negative refractive power, such that,upon varying a magnification, a distance between the first lens groupand the second lens group being varied, a distance between the secondlens group and the third lens group being varied, and a distance betweenthe third lens group and the fourth lens group being varied, uponfocusing from an infinite distance object to a close distance object,the fourth lens group being moved; and the following conditionalexpressions (1) and (2) being satisfied:0.55<f2/f4<1.40  (1)1.40<f1/fw<2.80  (2)

where f1 denotes a focal length of the first lens group; f2 denotes afocal length of the second lens group; f4 denotes a focal length of thefourth lens group; and fw denotes a focal length of the variablemagnification optical system in the wide angle end state.

Thus, it is possible to manufacture a variable magnification opticalsystem whose focusing lens group is compact in size and reduced inweight, thereby high speed and quiet focusing being effected withoutlens barrel being made large in size, and further by which variations inaberrations upon varying magnification from the wide angle end state tothe telephoto end state as well as variations in aberrations uponfocusing from the infinite distance object to the close distance objectcan be superbly suppressed.

Hereinafter, Examples of the variable magnification optical systemaccording to the embodiment of the present application will be describedwith reference to the accompanying drawings.

First Example

FIG. 1 is a sectional view, showing the variable magnification opticalsystem according to the First Example. Meanwhile, arrows in FIG. 1 andin FIG. 5, FIG. 9 and FIG. 13 described later show movement trajectoriesof the respective lens groups upon varying magnification from the wideangle end state (W) to the telephoto end state (T).

The variable magnification optical system according to the First Exampleis composed of, in order from an object side, a first lens group G1having positive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having positive refractivepower, a fourth lens group G4 having negative refractive power, and afifth lens group G5 having positive refractive power.

The first lens group G1 consists of, in order from the object side, apositive meniscus lens L11 having a convex surface facing the objectside, and a cemented positive lens constructed by a negative meniscuslens L12 having a convex surface facing the object side cemented with apositive meniscus lens L13 having a convex surface facing the objectside.

The second lens group G2 consists of, in order from the object side, anegative meniscus lens L21 having a convex surface facing the objectside, a cemented positive lens constructed by a positive meniscus lensL22 having a convex surface facing the object side cemented with anegative meniscus lens L23 having a convex surface facing the objectside, and a double concave negative lens L24.

The third lens group G3 consists of, in order from the object side, adouble convex positive lens L31, a cemented negative lens constructed bya double convex positive lens L32 cemented with double concave negativelens L33, an aperture stop S, a cemented negative lens constructed by apositive meniscus lens L34 having a concave surface facing the objectside cemented with a double concave negative lens L35, and a cementedpositive lens constructed by a double concave negative lens L36 cementedwith a double convex positive lens L37, and a double convex positivelens L38.

The fourth lens group G4 consists of, in order from the object side, apositive meniscus lens L41 having a concave surface facing the objectside and a double concave negative lens L42.

The fifth lens group G5 consists of a positive meniscus lens L51 havinga convex surface facing the object side.

In the variable magnification optical system according to the FirstExample, upon varying magnification from the wide angle end state to thetelephoto end state, the second lens group G2 and the fourth lens groupG4 are moved along the optical axis such that a distance between thefirst lens group G1 and the second lens group G2, a distance between thesecond lens group G2 and the third lens group G3, a distance between thethird lens group G3 and the fourth lens group G4 and a distance betweenthe fourth lens group G4 and the fifth lens group G5, are varied. Atthat time, the first lens group G1, the third lens group G3 and thefifth lens group G5 are fixed in positions with respect to the imageplane I.

In the variable magnification optical system according to the FirstExample, focusing from the infinite distance object to the closedistance object is carried out by moving the fourth lens group G4 as afocusing lens group toward the image side along the optical axis.

Also in the variable magnification optical system according to the FirstExample, the cemented negative lens constructed by the positive meniscuslens L34 and the negative lens L35, is moved as a vibration reductionlens to have a displacement component in a direction perpendicular tothe optical axis, thereby carrying out vibration reduction.

Here, in a lens system in which an entire lens system has a focal lengthof f, and a vibration reduction coefficient, which is a ratio of amoving amount of an image on the image plane I to that of the vibrationreduction lens group perpendicularly to the optical axis upon conductingvibration reduction, is K, in order to correct rotational camera shakeof an angle θ, the vibration reduction lens group for correcting thecamera shake may be moved by the amount of (f·tan θ)/K in a directionperpendicular to the optical axis.

In the wide-angle end state in the First Example, the vibrationreduction coefficient is 1.63, and the focal length is 72.10 (mm), sothat the moving amount of the vibration reduction lens group forcorrecting a rotational camera shake of 0.30 degrees is 0.23 (mm). Inthe telephoto end state, the vibration reduction coefficient is 1.70,and the focal length is 194.00 (mm), so that the moving amount of thevibration reduction lens group for correcting a rotational camera shakeof 0.20 degrees is 0.40 (mm).

Table 1

Table 1 below shows various values associated with the variablemagnification optical system according to the First Example.

In Table 1, f denotes a focal length, and BF denotes a back focal length(that is, a distance between a most image side lens surface and theimage plane I).

In [Surface Data], m denotes an order of an optical surface counted fromthe object side, r denotes a radius of curvature, d denotes asurface-to-surface distance (an interval from an n-th surface to an(n+1)-th surface, where n is an integer), nd denotes refractive indexfor d-line (wavelength λ=587.6 nm) and vd denotes an Abbe number ford-line (wavelength λ=587.6 nm). Further, OP denotes an object surface,variable denotes a variable surface to surface distance, Stop S denotesan aperture stop S, and I denotes the image plane. Meanwhile, a radiusof curvature r=∞ denotes a plane surface. Refractive index of airnd=1.00000 is omitted in the description.

In [Various Data], FNO denotes an F-number, 2ω denotes an angle of view(unit “°”), Ymax denotes a maximum image height, TL denotes a totallength of the variable magnification optical system (a distance on theoptical axis from the first surface to the image plane I), and dodenotes a variable interval between an n-th surface and an (n+1)-thsurface. Meanwhile, W denotes the wide-angle end state, M denotes anintermediate focal length state, and T denotes the telephoto end state.ID denotes infinite distance upon focusing the infinite distance object,and CD denotes close distance upon focusing on a close distance object.

In [Lens Group Data], a starting surface ST and a focal length f areshown for each lens group.

In [Values for Conditional Expressions], values corresponding torespective conditional expressions in the variable magnification opticalsystem according to the First Example are shown.

It is noted, here, that “mm” is generally used for the unit of lengthsuch as the focal length f, the radius of curvature r and the unit forother lengths shown in Table 1. However, since similar opticalperformance can be obtained by an optical system proportionally enlargedor reduced, the unit is not necessarily to be limited to “mm”.

The above-mentioned reference symbols in Table 1 are also employed inthe same manner in Tables of the after-mentioned Examples.

TABLE 1 First Example [Surface Data] m r d nd νd OP ∞  1 127.6244 5.5341.48749 70.31  2 1322.7608 0.200  3 99.4549 1.700 1.80610 33.34  462.2096 10.428  1.49700 81.73  5 3849.3448 variable  6 312.0349 1.0001.77250 49.62  7 39.3277 8.235  8 38.7701 3.919 1.84666 23.80  9103.1681 1.000 1.80400 46.60 10 48.5499 4.120 11 −74.2974 1.000 1.6031160.69 12 649.2745 variable 13 44.7829 5.265 1.72342 38.03 14 −98.44961.019 15 50.5480 5.402 1.49700 81.73 16 −45.6249 1.000 1.90200 25.26 17295.6528 2.002 18(Stop S) ∞ 8.326 19 −54.0959 3.659 1.80518 25.45 20−21.1959 1.000 1.66755 41.87 21 58.7139 4.250 22 −156.1142 1.000 1.9036631.27 23 28.3088 5.794 1.61800 63.34 24 −40.0487 0.200 25 36.9605 4.3161.79952 42.09 26 −382.7973 variable 27 −306.2135 2.700 1.71736 29.57 28−50.1498 0.809 29 −55.5576 1.000 1.69680 55.52 30 30.3235 variable 3150.3470 3.397 1.60300 65.44 32 133.9533 BF I ∞ [Various Data] VariableMagnification Ratio 2.69 W M T f 72.1 99.9 194.0 FNO 4.05 4.11 4.15 2ω33.86 24.12 12.32 Ymax 21.60 21.60 21.60 TL 218.32 218.32 218.32 BF53.32 53.32 53.32 W M T W M T ID ID ID CD CD CD d5 2.000 19.906 51.6272.000 19.906 51.627 d12 51.627 33.721 2.000 51.627 33.721 2.000 d263.000 5.594 7.658 3.569 6.412 9.301 d30 20.101 17.507 15.442 19.53216.689 13.800 [Lens Group Data] Group ST f 1 1 154.325 2 6 −45.859 3 1345.676 4 27 −42.922 5 31 131.760 [Values for Conditional Expressions](1) f2/f4 = 1.068 (2) f1/fw = 2.140 (3)(−f2)/f3 = 1.004 (4) f1/(−f2) =3.365 (5) fP/(−fN) = 2.971 (6) |fvr|/f3 = 1.097

FIGS. 2A, 2B and 2C are graphs showing various aberrations of thevariable magnification optical system according to the First Exampleupon focusing on an infinite distance object, in the wide-angle endstate, in the intermediate focal length state, and in the telephoto endstate, respectively.

FIGS. 3A and 3B are, respectively, with respect to the variablemagnification optical system according to the First Example, graphsshowing meridional transverse aberrations at the time when vibrationreduction is carried out for correcting rotational camera shake of 0.30degrees upon focusing on the infinite distance object in the wide angleend state, and meridional transverse aberrations at the time whenvibration reduction is carried out for correcting rotational camerashake of 0.20 degrees upon focusing on the infinite distance object inthe telephoto end state.

FIGS. 4A, 4B and 4C are, respectively, graphs showing variousaberrations of the variable magnification optical system according tothe First Example upon focusing on a close distance object, in whichFIG. 4A is in the wide-angle end state, FIG. 4B is in the intermediatefocal length state, and FIG. 4C is in the telephoto end state.

In respective graphs, FNO denotes an F-number, Y denotes an imageheight, and NA denotes numerical aperture. In detail, in the graph ofspherical aberration, a value of F-number FNO corresponding to themaximum aperture is shown, or a value of numerical aperture NA is shown.In the graph of astigmatism and the graph of distortion, the maximumvalues of the image height Y are respectively shown. In the graph ofcoma aberration, values of respective image heights are shown. Inrespective graphs of aberrations, d denotes an aberration curve atd-line (wavelength λ=587.6 nm), and g denotes an aberration curve atg-line (wavelength λ=435.8 nm). In the graph showing astigmatism, asolid line indicates a sagittal image plane, and a broken line indicatesa meridional image plane. In the graph of coma aberration, comaaberrations at respective image heights Y are shown.

Incidentally, the above-described explanation regarding variousaberration graphs is the same with respect to the other Examplesdescribed hereinafter.

As is apparent from the respective graphs, the variable magnificationoptical system according to the present Example has superb opticalperformance as a result of good corrections to various aberrations fromthe wide-angle end state to the telephoto end state, and furtherexcellent optical performance even upon carrying out vibration reductionas well as upon focusing on a close distance object.

Second Example

FIG. 5 is a sectional view showing the variable magnification opticalsystem according to the Second Example.

The variable magnification optical system according to the SecondExample is composed of, in order from an object side, a first lens groupG1 having positive refractive power, a second lens group G2 havingnegative refractive power, a third lens group G3 having positiverefractive power, a fourth lens group G4 having negative refractivepower and a fifth lens group G5 having positive refractive power.

The first lens group G1 consists of, in order from the object side, apositive meniscus lens L11 having a convex surface facing the objectside, and a cemented positive lens constructed by a negative meniscuslens L12 having a convex surface facing the object side cemented with adouble convex positive lens L13.

The second lens group G2 consists of, in order from the object side, anegative meniscus lens L21 having a convex surface facing the objectside, a cemented positive lens constructed by a positive meniscus lensL22 having a convex surface facing the object side cemented with anegative meniscus lens L23 having a convex surface facing the objectside, and a double concave negative lens L24.

The third lens group G3 consists of, in order from the object side, adouble convex positive lens L31, a double convex positive lens L32, acemented negative lens constructed by a double convex positive lens L33cemented with a double concave negative lens L34, an aperture stop S, acemented negative lens constructed by a positive meniscus lens L35having a concave surface facing the object side cemented with a doubleconcave negative lens L36, a cemented negative lens constructed by adouble concave negative lens L37 cemented with a double convex positivelens L38, and a double convex positive lens L39.

The fourth lens group G4 consists of, in order from the object side, apositive meniscus lens L41 having a concave surface facing the objectside and a double concave negative lens L42.

The fifth lens group G5 consists of a positive meniscus lens L51 havinga convex surface facing the object side.

In the variable magnification optical system according to the SecondExample, upon varying magnification from the wide angle end state to thetelephoto end state, the second lens group G2 and the fourth lens groupG4 are moved along the optical axis such that a distance between thefirst lens group G1 and the second lens group G2, a distance between thesecond lens group G2 and the third lens group G3, a distance between thethird lens group G3 and the fourth lens group G4 and a distance betweenthe fourth lens group G4 and the fifth lens group G5, are varied. Atthat time, the first lens group G1, the third lens group G3 and thefifth lens group G5 are fixed in positions with respect to the imageplane I.

In the variable magnification optical system according to the SecondExample, focusing from the infinite distance object to the closedistance object is carried out by moving the fourth lens group G4 as afocusing lens group toward the image side along the optical axis.

In the variable magnification optical system according to the SecondExample, the cemented negative lens constructed by the positive meniscuslens L35 and the negative lens L36, is moved as a vibration reductionlens to have a displacement component in a direction perpendicular tothe optical axis, thereby carrying out vibration reduction.

Here, in the variable magnification optical system according to theSecond Example, the vibration reduction coefficient in the wide-angleend state is 1.62, and the focal length is 72.10 (mm), so that themoving amount of the vibration reduction lens group for correcting arotational camera shake of 0.30 degrees is 0.23 (mm). In the telephotoend state, the vibration reduction coefficient is 1.70, and the focallength is 194.00 (mm), so that the moving amount of the vibrationreduction lens group for correcting a rotational camera shake of 0.20degrees is 0.40 (mm).

Table 2 below shows various values associated with the variablemagnification optical system according to the Second Example.

TABLE 2 Second Example [Surface Data] m r d nd νd OP ∞  1 131.1214 5.4491.48749 70.31  2 1109.4966 0.200  3 98.0798 1.700 1.80610 33.34  461.5920 10.521  1.49700 81.73  5 −7105.2636 variable  6 380.8979 1.0001.77250 49.62  7 38.2124 6.936  8 38.1827 4.034 1.84666 23.80  9101.8431 1.000 1.80400 46.60 10 49.6281 4.170 11 −75.5321 1.000 1.6031160.69 12 631.4782 variable 13 43.3989 5.088 1.60300 65.44 14 −128.04340.200 15 71.7117 2.953 1.84666 23.80 16 1360.1055 1.671 17 59.5261 4.6611.49700 81.73 18 −46.7718 1.000 1.90200 25.26 19 84.5350 1.820 20(StopS) ∞ 6.448 21 −52.0090 3.604 1.80518 25.45 22 −20.4107 1.000 1.6675541.87 23 58.3221 4.156 24 −188.8475 1.000 1.90366 31.27 25 27.1167 5.5051.61800 63.34 26 −46.5152 0.200 27 39.9140 4.500 1.79952 42.09 28−111.0815 variable 29 −249.2850 2.700 1.71736 29.57 30 −47.0764 0.828 31−51.1491 1.000 1.69680 55.52 32 31.0004 variable 33 55.1958 3.4871.60300 65.44 34 197.9712 BF I ∞ [Various Data] Variable MagnificationRatio 2.69 W M T f 72.1 99.9 194.0 FNO 4.05 4.12 4.17 2ω 33.82 24.0812.30 Ymax 21.60 21.60 21.60 TL 218.32 218.32 218.32 BF 53.32 53.3253.32 W M T W M T ID ID ID CD CD CD d5 2.000 19.764 51.257 2.000 19.76451.257 d12 51.257 33.494 2.000 51.257 33.494 2.000 d28 3.000 5.617 7.6573.569 6.435 9.297 d32 20.913 18.296 16.256 20.344 17.479 14.616 [LensGroup Data] Group ST f 1 1 152.488 2 6 −45.554 3 13 45.955 4 29 −42.5955 33 125.767 [Values for Conditional Expressions] (1) f2/f4 = 1.069 (2)f1/fw = 2.115 (3)(−f2)/f3 = 0.991 (4) f1/(−f2) = 3.347 (5) fP/(−fN) =2.919 (6) |fvr|/f3 = 1.067

FIGS. 6A, 6B and 6C are graphs showing various aberrations of thevariable magnification optical system according to the Second Exampleupon focusing on an infinite distance object, in the wide-angle endstate, in the intermediate focal length state, and in the telephoto endstate, respectively.

FIGS. 7A and 7B are, respectively, with respect to the variablemagnification optical system according to the Second Example, graphsshowing meridional transverse aberrations at the time when vibrationreduction is carried out for correcting rotational camera shake of 0.30degrees upon focusing on the infinite distance object in the wide angleend state, and meridional transverse aberrations at the time whenvibration reduction is carried out for correcting rotational camerashake of 0.20 degrees upon focusing on the infinite distance object inthe telephoto end state.

FIGS. 8A, 8B and 8C are, respectively, graphs showing variousaberrations of the variable magnification optical system according tothe Second Example upon focusing on a close distance object, in whichFIG. 8A is in the wide-angle end state, FIG. 8B is in the intermediatefocal length state, and FIG. 8C is in the telephoto end state.

As is apparent from the respective graphs, the variable magnificationoptical system according to the present Example has superb opticalperformance as a result of good corrections to various aberrations fromthe wide-angle end state to the telephoto end state, and furtherexcellent optical performance even upon carrying out vibration reductionas well as upon focusing on a close distance object.

Third Example

FIG. 9 is a sectional view, showing the variable magnification opticalsystem according to the Third Example.

The variable magnification optical system according to the Third Exampleis composed of, in order from an object side, a first lens group G1having positive refractive power, a second lens group G2 having negativerefractive power, a third lens group G3 having positive refractivepower, a fourth lens group G4 having negative refractive power and afifth lens group G5 having positive refractive power.

The first lens group G1 consists of, in order from the object side, apositive meniscus lens L11 having a convex surface facing the objectside, and a cemented positive lens constructed by a negative meniscuslens L12 having a convex surface facing the object side cemented with adouble convex positive lens L13.

The second lens group G2 consists of, in order from the object side, anegative meniscus lens L21 having a convex surface facing the objectside, a cemented negative lens constructed by a double concave negativelens L22 having a convex surface facing the object side cemented with apositive meniscus lens L23 having a convex surface facing the objectside, and a negative meniscus lens L24 having a concave surface facingthe object side.

The third lens group G3 consists of, in order from the object side, adouble convex positive lens L31, a cemented negative lens constructed bya double convex positive lens L32 cemented with a double concavenegative lens L33, an aperture stop S, a cemented negative lensconstructed by a positive meniscus lens L34 having a concave surfacefacing the object side cemented with a double concave negative lens L35,a cemented positive lens constructed by a negative meniscus lens L36having a concave surface facing the object side cemented with a doubleconvex positive lens L37, and a double convex positive lens L39.

The fourth lens group G4 consists of, in order from the object side, apositive meniscus lens L41 having a concave surface facing the objectside and a double concave negative lens L42.

The fifth lens group G5 consists of a positive meniscus lens L51 havinga convex surface facing the object side.

In the variable magnification optical system according to the ThirdExample, upon varying magnification from the wide angle end state to thetelephoto end state, the second lens group G2 and the fourth lens groupG4 are moved along the optical axis such that a distance between thefirst lens group G1 and the second lens group G2, a distance between thesecond lens group G2 and the third lens group G3, a distance between thethird lens group G3 and the fourth lens group G4 and a distance betweenthe fourth lens group G4 and the fifth lens group G5, are varied.Meanwhile, at this time, the first lens group G1, the third lens groupG3 and fifth lens group G5 are fixed in positions with respect to theimage plane I.

In the variable magnification optical system according to the ThirdExample, focusing from the infinite distance object to the closedistance object is carried out by moving the fourth lens group G4 as afocusing lens group toward the image side along the optical axis.

In the variable magnification optical system according to the ThirdExample, the cemented negative lens constructed by the positive meniscuslens L34 and the negative lens L35 is moved as a vibration reductionlens to have a displacement component in a direction perpendicular tothe optical axis, thereby carrying out vibration reduction.

Here, in the wide-angle end state in the Third Example, the vibrationreduction coefficient is 1.63, and the focal length is 72.10 (mm), sothat the moving amount of the vibration reduction lens group forcorrecting a rotational camera shake of 0.30 degrees is 0.23 (mm). Inthe telephoto end state, the vibration reduction coefficient is 1.70,and the focal length is 194.00 (mm), so that the moving amount of thevibration reduction lens group for correcting a rotational camera shakeof 0.20 degrees is 0.40 (mm).

Table 3 below shows various values associated with the variablemagnification optical system according to the Third Example.

TABLE 3 Third Example [Surface Data] m r d nd νd OP ∞  1 141.1591 4.5001.48749 70.31  2 543.1898 0.200  3 85.6758 2.000 1.80610 33.34  457.2066 11.246  1.49700 81.73  5 −1626.1596 variable  6 93.2280 2.0001.83400 37.18  7 41.8983 8.938  8 −115.2692 2.000 1.69680 55.52  944.2262 4.356 1.84666 23.80 10 27715.4320 2.322 11 −55.6670 1.5001.80400 46.60 12 −129.1012 variable 13 49.0208 4.818 1.80100 34.92 14−105.6641 0.200 15 48.2516 5.297 1.49700 81.73 16 −49.0156 1.300 1.9020025.26 17 127.8612 2.373 18(Stop S) ∞ 9.279 19 −58.0260 3.765 1.8051825.45 20 −21.3498 1.200 1.66755 41.87 21 55.2645 3.937 22 953.3728 1.2001.90366 31.27 23 28.8503 5.672 1.60300 65.44 24 −48.6329 0.200 2536.9235 4.531 1.77250 49.62 26 −308.8274 variable 27 −687.7351 2.7001.71736 29.57 28 −56.8272 0.787 29 −65.5667 1.000 1.69680 55.52 3028.2486 variable 31 41.4926 3.492 1.60300 65.44 32 88.2133 BF I ∞[Various Data] Variable Magnification Ratio 2.69 W M T f 72.1 99.9 194.0FNO 4.09 4.13 4.16 2ω 34.18 24.28 12.40 Ymax 21.60 21.60 21.60 TL 218.32218.32 218.32 BF 55.22 55.22 55.22 W M T W M T ID ID ID CD CD CD d52.000 18.794 48.567 2.000 18.794 48.567 d12 48.567 31.773 2.000 48.56731.773 2.000 d26 3.920 6.471 7.964 4.497 7.299 9.612 d30 17.798 15.24713.754 17.221 14.419 12.106 [Lens Group Data] Group ST f 1 1 145.325 2 6−43.336 3 13 45.621 4 27 −42.711 5 31 126.368 [Values for ConditionalExpressions] (1) f2/f4 = 1.015 (2) f1/fw = 2.016 (3)(−f2)/f3 = 0.950 (4)f1/(−f2) = 3.353 (5) fP/(−fN) = 3.056 (6) |fvr|/f3 = 1.111

FIGS. 10A, 10B and 10C are graphs showing various aberrations of thevariable magnification optical system according to the Third Exampleupon focusing on an infinite distance object, in the wide-angle endstate, in the intermediate focal length state, and in the telephoto endstate, respectively. FIGS. 11A and 11B are, respectively, with respectto the variable magnification optical system according to the ThirdExample, graphs showing meridional transverse aberrations at the timewhen vibration reduction is carried out for correcting rotational camerashake of 0.30 degrees upon focusing on the infinite distance object inthe wide angle end state, and meridional transverse aberrations at thetime when vibration reduction is carried out for correcting rotationalcamera shake of 0.20 degrees upon focusing on the infinite distanceobject in the telephoto end state.

FIGS. 12A, 12B and 12C are, respectively, graphs showing variousaberrations of the variable magnification optical system according tothe Third Example upon focusing on a close distance object, in whichFIG. 12A is in the wide-angle end state, FIG. 12B is in the intermediatefocal length state, and FIG. 12C is in the telephoto end state.

As is apparent from the respective graphs, the variable magnificationoptical system according to the present Example has superb opticalperformance as a result of good corrections to various aberrations fromthe wide-angle end state to the telephoto end state, and furtherexcellent optical performance even upon carrying out vibration reductionas well as upon focusing on a close distance object.

Fourth Example

FIG. 13 is a sectional view, showing the variable magnification opticalsystem according to the Fourth Example.

The variable magnification optical system according to the FourthExample is composed of, in order from an object side, a first lens groupG1 having positive refractive power, a second lens group G2 havingnegative refractive power, a third lens group G3 having positiverefractive power, and a fourth lens group G4 having negative refractivepower.

The first lens group G1 consists of, in order from the object side, apositive meniscus lens L11 having a convex surface facing the objectside, and a cemented positive lens constructed by a negative meniscuslens L12 having a convex surface facing the object side cemented with apositive meniscus lens L13 having a convex surface facing the objectside.

The second lens group G2 consists of, in order from the object side, anegative meniscus lens L21 having a convex surface facing the objectside, a cemented positive lens constructed by a positive meniscus lensL22 having a convex surface facing the object side cemented with anegative meniscus lens L23 having a convex surface facing the objectside, and a double concave negative lens L24.

The third lens group G3 consists of, in order from the object side, adouble convex positive lens L31, a cemented negative lens constructed bya double convex positive lens L32 cemented with a double concavenegative lens L33, an aperture stop S, a cemented negative lensconstructed by a positive meniscus lens L34 having a concave surfacefacing the object side cemented with a double concave negative lens L35,a cemented positive lens constructed by a double concave negative lensL36 cemented with a double convex positive lens L37, and a double convexpositive lens L38.

The fourth lens group G4 consists of, in order from the object side, adouble convex positive lens L41 and a double concave negative lens L42.

In the variable magnification optical system according to the FourthExample, upon varying magnification from the wide angle end state to thetelephoto end state, the second lens group G2 and the fourth lens groupG4 are moved along the optical axis such that a distance between thefirst lens group G1 and the second lens group G2, a distance between thesecond lens group G2 and the third lens group G3, and a distance betweenthe third lens group G3 and the fourth lens group G4, are varied.Meanwhile, at that time, the first lens group G1 and the third lensgroup G3 are fixed in positions with respect to the image plane I.

In the variable magnification optical system according to the FourthExample, focusing from the infinite distance object to the closedistance object is carried out by moving the fourth lens group G4 as afocusing lens group toward the image side along the optical axis.

In the variable magnification optical system according to the FourthExample, the cemented negative lens constructed by the positive meniscuslens L34 and the negative lens L35, is moved as a vibration reductionlens to have a displacement component in a direction perpendicular tothe optical axis, thereby carrying out vibration reduction.

Here, in the wide-angle end state of the variable magnification opticalsystem according to the Fourth Example, the vibration reductioncoefficient is 1.68, and the focal length is 72.10 (mm), so that themoving amount of the vibration reduction lens group for correcting arotational camera shake of 0.30 degrees is 0.22 (mm). In the telephotoend state, the vibration reduction coefficient is 1.70, and the focallength is 194.00 (mm), so that the moving amount of the vibrationreduction lens group for correcting a rotational camera shake of 0.20degrees is 0.40 (mm).

Table 4 below shows various values associated with the variablemagnification optical system according to the Fourth Example.

TABLE 4 Fourth Example [Surface Data] m r d nd νd OP ∞  1 122.9116 5.3641.48749 70.31  2 642.7135 0.200  3 93.7360 1.700 1.80610 33.34  460.6328 10.593  1.49700 81.73  5 4543.6426 variable  6 289.4140 1.0001.77250 49.62  7 37.2424 9.821  8 38.9626 3.720 1.84666 23.80  9 91.21651.000 1.80400 46.60 10 52.4749 3.560 11 −100.3987 1.000 1.60311 60.69 12253.6299 variable 13 44.5612 5.223 1.66446 35.87 14 −90.1338 0.200 1559.0915 5.257 1.49700 81.73 16 −42.3802 1.000 1.90200 25.26 17 593.63781.136 18(Stop S) ∞ 6.982 19 −54.8344 3.877 1.80518 25.45 20 −21.31121.420 1.66755 41.87 21 63.0651 4.382 22 −154.1165 1.000 1.90366 31.27 2334.7644 5.687 1.60300 65.44 24 −40.7282 0.200 25 46.6093 4.036 1.8040046.60 26 −182.7333 variable 27 191.1371 2.700 1.84666 23.80 28 −192.11841.091 29 −151.1748 1.000 1.61772 49.81 30 34.1179 BF I ∞ [Various Data]Variable Magnification Ratio 2.69 W M T f 72.1 99.7 194.0 FNO 4.14 4.174.17 2ω 33.30 23.84 12.20 Ymax 21.60 21.60 21.60 TL 218.32 218.32 218.32BF 77.52 74.71 75.11 W M T W M T ID ID ID CD CD CD d5 2.000 20.20552.654 2.000 20.205 52.654 d12 52.654 34.449 2.000 52.654 34.449 2.000d26 3.000 5.810 5.410 3.821 7.008 7.750 [Lens Group Data] Group ST f 1 1150.995 2 6 −48.062 3 13 47.483 4 27 −77.084 [Values for ConditionalExpressions] (1) f2/f4 = 0.624 (2) f1/fw = 2.094 (3)(−f2)/f3 = 1.012 (4)f1/(−f2 ) = 3.142 (5) fP/(−fN) = 2.525 (6) |fvr|/f3 = 1.108

FIGS. 14A, 14B and 14C are graphs showing various aberrations of thevariable magnification optical system according to the Fourth Exampleupon focusing on an infinite distance object, in the wide-angle endstate, in the intermediate focal length state, and in the telephoto endstate, respectively. FIGS. 15A and 15B are, respectively, with respectto the variable magnification optical system according to the FourthExample, graphs showing meridional transverse aberrations at the timewhen vibration reduction is carried out for correcting rotational camerashake of 0.30 degrees upon focusing on the infinite distance object inthe wide angle end state, and meridional transverse aberrations at thetime when vibration reduction is carried out for correcting rotationalcamera shake of 0.20 degrees upon focusing on the infinite distanceobject in the telephoto end state.

FIGS. 16A, 16B and 16C are, respectively, graphs showing variousaberrations of the variable magnification optical system according tothe Fourth Example upon focusing on a close distance object, in whichFIG. 16A is in the wide-angle end state, FIG. 16B is in the intermediatefocal length state, and FIG. 16C is in the telephoto end state.

As is apparent from the respective graphs, the variable magnificationoptical system according to the present Example has superb opticalperformance as a result of good corrections to various aberrations fromthe wide-angle end state to the telephoto end state, and furtherexcellent optical performance even upon carrying out vibration reductionas well as upon focusing on a close distance object.

With such construction according to each Example described above, it ispossible to realize a variable magnification optical system whosefocusing lens group is compact in size and reduced in weight, so highspeed and quiet focusing can be effected without lens barrel being madelarge in size, and further by which variations in aberrations uponvarying magnification from the wide angle end state to the telephoto endstate as well as variations in aberrations upon focusing from theinfinite distance object to the close distance object can be superblysuppressed.

Meanwhile, each of the above described Example is a concrete example ofthe invention of the present application, and the invention of thepresent application is not limited to them. The contents described belowcan be adopted without deteriorating an optical performance of thevariable magnification optical systems of the present application.

Although the variable magnification optical systems each having fourgroup or five group configuration were illustrated above as numericalexamples of the variable magnification optical systems of the presentembodiment, the present application is not limited to them and thevariable magnification optical systems having other configurations (suchas six group configuration and the like) can be configured. Concretely,a lens configuration that a lens or a lens group is added to the mostobject side of the variable magnification optical system of each Exampleis possible, and a lens configuration that a lens or a lens group isadded to the most image side of the variable magnification opticalsystem of the present application is also possible.

Further, in the variable magnification optical system according to eachExample, the fourth lens group in the entirety thereof is made as afocusing lens group, but a portion of any lens group or a plurality oflens groups may be made as a focusing lens group. It is preferable thatthe focusing lens group has positive refractive power. It is morepreferable that the focusing lens group consists of two lenses. Thefocusing lens group can be used for auto focus, and suitable for beingdriven by a motor for auto focus such as an ultrasonic motor, steppingmotor, VCM motor or the like, and it is possible to realize high speedauto focus and quiet auto focus superbly.

Further, in the variable magnification optical system according to eachExample described above, a portion of the third lens group is made as avibration reduction lens group, but any lens group in the entiretythereof or in a portion thereof can be so moved, as a vibrationreduction lens group, to have a component in a direction perpendicularto the optical axis, or rotationally moved (swayed) in an intra-planedirection including the optical axis for conducting vibration reduction.Further, in the variable magnification optical system according to eachExample described above, it is not always necessary to have anyconfiguration for conducting vibration reduction.

Further, in the variable magnification optical system according to eachExample described above, it is preferable to arrange an aperture stop inthe third lens group, and a lens frame can substitute for the aperturestop without disposing a member as an aperture stop.

Further, in the variable magnification optical system according to eachExample described above, a lens surface of a lens may be a sphericalsurface, a plane surface, or an aspherical surface. Each lens may beformed of glass material, resin material or composite of glass materialand resin material. When a lens surface is a spherical surface or aplane surface, lens processing, assembling and adjustment become easy,and it is possible to prevent deterioration in optical performancecaused by errors in lens processing, assembling and adjustment, so thatit is preferable. Moreover, even if an image plane is shifted,deterioration in representation performance is little, so that it ispreferable. When a lens surface is an aspherical surface, the asphericalsurface may be fabricated by a grinding process, a glass molding processthat a glass material is formed into an aspherical shape by a mold, or acompound type process that a resin material on a glass lens surface isformed into an aspherical shape. A lens surface may be a diffractiveoptical surface, and a lens may be a graded-index type lens (GRIN lens)or a plastic lens.

Moreover, the lens surface(s) of the lenses configuring the variablemagnification optical system according to each Example described above,may be coated with anti-reflection coating(s). With this contrivance, itis feasible to reduce a flare as well as ghost and attain a high opticalperformance with high contrast. In particular, it is preferable that, inthe variable magnification optical system according to each Exampledescribed above, the second object side lens surface counted from themost object side may be applied with anti-reflection coating.

Next, a camera equipped with the variable magnification optical systemaccording to the present embodiment, will be explained with referring toFIG. 17.

FIG. 17 is a view showing a configuration of a camera equipped with thevariable magnification optical system according to the presentembodiment.

A camera 1 is a lens interchangeable type so-called mirror-less cameraequipped with the variable magnification optical system according to theFirst Example as an imaging lens 2, as shown in FIG. 17.

In the camera 1, light emitted from an unillustrated object (an objectto be imaged) is collected by the imaging lens 2, and forms an image ofthe object to be imaged on an imaging plane of an imaging part 3 throughan unillustrated OLPF (optical low pass filter). The image of the objectto be imaged is photo-electronically converted through aphoto-electronic conversion element provided in the imaging part 3 toform an object image. This object image is displayed on an EVF(electronic view finder) 4 provided on the camera 1. Thus, aphotographer can observe the object image through the EVF 4.

When the photographer presses an unillustrated release button, theobject image formed through the imaging part 3 is stored in anunillustrated memory. Thus, the photographer can take a picture of theobject to be imaged by the camera 1.

The variable magnification optical system according to the First Exampledescribed above is mounted on the camera 1 as the imaging lens 2,thereby the focusing lens group being made compact in size and reducedin weight, so that it is possible to realize a variable magnificationoptical system whose focusing lens group is compact in size and reducedin weight, so high speed and quiet focusing can be effected without lensbarrel being made large in size, and further by which variations inaberrations upon varying magnification from the wide angle end state tothe telephoto end state as well as variations in aberrations uponfocusing from the infinite distance object to the close distance objectcan be superbly suppressed.

Incidentally, even if the camera is so composed that the variablemagnification optical system according to the Second to Fourth Examplesis mounted on the camera as the imaging lens 2, the same effect can beattained as the camera 1. Moreover, the same effect as the above camera1 is attained even in the case where the variable magnification opticalsystem according to each of Examples as described, is mounted on asingle lens reflex-type camera which is provided with a quick returnmirror and in which an object to be imaged is observed through a finderoptical system.

Finally, an outline of a method for manufacturing a variablemagnification optical system according to the present embodiment isdescribed with referring to FIG. 18.

FIG. 18 is a view showing an outline of a method for manufacturing avariable magnification optical system according to the presentembodiment.

A method for manufacturing a variable magnification optical systemaccording to the present embodiment, shown in FIG. 18, comprises step S1of preparing, in order from an object side: a first lens group havingpositive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having negative refractive power; step S2 ofarranging the first to fourth lens groups such that, upon varying amagnification, a distance between the first lens group and the secondlens group is varied, a distance between the second lens group and thethird lens group is varied, and a distance between the third lens groupand the fourth lens group is varied; upon focusing from an infinitedistance object to a close distance object, the fourth lens group beingmoved; and the following conditional expressions (1) and (2) beingsatisfied:0.55<f2/f4<1.40  (1)1.40<f1/fw<2.80  (2)

where f1 denotes a focal length of the first lens group; f2 denotes afocal length of the second lens group; f4 denotes a focal length of thefourth lens group; and fw denotes a focal length of the variablemagnification optical system in the wide angle end state.

Thus, according to the method for manufacturing a variable magnificationoptical system of the present embodiment, it is possible to manufacturea variable magnification optical system whose focusing lens group iscompact in size and reduced in weight, thereby high speed and quietfocusing being effected without lens barrel being made large in size,and further by which variations in aberrations upon varyingmagnification from the wide angle end state to the telephoto end stateas well as variations in aberrations upon focusing from the infinitedistance object to the close distance object can be superbly suppressed.

EXPLANATION OF SYMBOLS

-   G1: first lens group-   G2: second lens group-   G3: third lens group-   G4: fourth lens group-   G5: fifth lens group-   S: aperture stop-   I: image plane

What is claimed is:
 1. A variable magnification optical systemcomprising, in order from an object side, a first lens group havingpositive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having negative refractive power; upon varying amagnification, a distance between the first lens group and the secondlens group being varied, a distance between the second lens group andthe third lens group being varied, and a distance between the third lensgroup and the fourth lens group being varied; upon focusing, the fourthlens group being moved; and the following conditional expressions beingsatisfied:0.55<f2/f4<1.401.40<f1/fw≤2.094 where f1 denotes a focal length of the first lensgroup, f2 denotes a focal length of the second lens group, f4 denotes afocal length of the fourth lens group, and fw denotes a focal length ofthe variable magnification optical system in the wide angle end state.2. The variable magnification optical system according to claim 1,wherein the following conditional expression is satisfied:0.82<(−f2)/f3<1.30 where f3 denotes a focal length of the third lensgroup.
 3. The variable magnification optical system according to claim1, wherein the following conditional expression is satisfied:2.00<f1/(−f2)<4.00.
 4. The variable magnification optical systemaccording to claim 1, wherein the fourth lens group consists of, inorder from the object side, a positive lens and a negative lens.
 5. Thevariable magnification optical system according to claim 4, wherein thefollowing conditional expression is satisfied:2.20<fP/(−fN)<3.70 where fP denotes a focal length of the positive lensin the fourth lens group, and fN denotes a focal length of the negativelens in the fourth lens group.
 6. The variable magnification opticalsystem according to claim 1, wherein, upon varying a magnification, thefirst lens group is fixed in position, with respect to the image plane.7. The variable magnification optical system according to claim 1,wherein, upon varying a magnification, the third lens group is fixed inposition, with respect to the image plane.
 8. The variable magnificationoptical system according to claim 1, wherein the first lens groupcomprises, in order from the object side, a positive lens, a negativelens and a positive lens.
 9. The variable magnification optical systemaccording to claim 1, comprises a vibration reduction lens group that ismovable to have a displacement component in a direction perpendicular tothe optical axis.
 10. The variable magnification optical systemaccording to claim 9, wherein the following conditional expression issatisfied:0.70<|fvr|/f3<1.60 where fvr denotes a focal length of the vibrationreduction lens group.
 11. An optical equipment comprising a variablemagnification optical system according to claim
 1. 12. An imagingequipment equipped with a variable magnification optical systemaccording to claim 1, and an imaging portion picking up an image formedby the variable magnification optical system.
 13. A method formanufacturing a variable magnification optical system, comprising thesteps of arranging, in order from an object side, a first lens grouphaving positive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having negative refractive power such that, uponvarying a magnification, a distance between the first lens group and thesecond lens group is varied, a distance between the second lens groupand the third lens group is varied, and a distance between the thirdlens group and the fourth lens group is varied; and upon focusing, thefourth lens group being moved; the method further comprising one of thefollowing features A and B: the feature A comprising: satisfying thefollowing conditional expressions:0.55<f2/f4<1.401.40<f1/fw≤2.094 where f1 denotes a focal length of the first lensgroup, f2 denotes a focal length of the second lens group, f4 denotes afocal length of the fourth lens group, and fw denotes a focal length ofthe variable magnification optical system in the wide angle end state,and the feature B comprising: arranging the third lens group to be fixedin position with respect to the image plane upon varying amagnification; and satisfying the following conditional expressions:1.40<f1/fw<2.802.00<f1/(−f2)<3.50 where f1 denotes focal length of the first lensgroup, f2 denotes a focal length of the second lens group, and fwdenotes a focal length of the variable magnification optical system inthe wide angle end state.
 14. A variable magnification optical systemcomprising, in order from an object side, a first lens group havingpositive refractive power, a second lens group having negativerefractive power, a third lens group having positive refractive power,and a fourth lens group having negative refractive power; upon varying amagnification, a distance between the first lens group and the secondlens group being varied, a distance between the second lens group andthe third lens group being varied, and a distance between the third lensgroup and the fourth lens group being varied; upon focusing, the fourthlens group being moved; upon varying a magnification, the third lensgroup being fixed in position, with respect to the image plane; and thefollowing conditional expressions being satisfied:1.40<f1/fw<2.802.00<f1/(−f2)<3.50 where f1 denotes a focal length of the first lensgroup, f2 denotes a focal length of the second lens group, and fwdenotes a focal length of the variable magnification optical system inthe wide angle end state.
 15. The variable magnification optical systemaccording to claim 14, wherein the first lens group comprises, in orderfrom the object side, a positive lens, a negative lens and a positivelens.
 16. The variable magnification optical system according to claim14, comprises a vibration reduction lens group that is movable to have adisplacement component in a direction perpendicular to the optical axis.17. The variable magnification optical system according to claim 16,wherein the following conditional expression is satisfied:0.70<|fvr|/f3<1.60 where fvr denotes a focal length of the vibrationreduction lens group.
 18. An optical equipment comprising a variablemagnification optical system according to claim 14.